The conventional muzzle-loading rifle includes a barrel which extends forwardly from a receiver, the rearward end of the barrel having a breech which receives propellant and a projectile through the muzzle. A breech plug is threadably mounted in the receiver and seals the rearward end of the barrel, in the breech, to prevent blow back of gases upon ignition of the propellant within the breech.
In all percussion muzzle-loaders, a nipple is mounted in the rear end of the breech plug with a projecting rearward end adapted to receive a percussion cap thereon. When struck by a hammer, the percussion cap is fired and ignition sparks travel through a central bore the length of the nipple to ignite the propellant in the breech.
One problem with conventional nipples is that they provide a poor seal between the percussion cap and the nipple because conventionally the cap is formed of copper and the nipple is formed of steel. The cap splits when fired, allowing blow-by of gases from the firearm and permitting the discharge of residue into the receiver and around the bolt firing pin and hammer.
Another problem with blow-by gas in conventional breech plugs with nipples is the possibility of percussion cap particles being discharged out of the receiver and into the face of the shooter.
The use of a cap on the rearward end of a nipple to provide the primer for the ignition system requires effective seating of the cap on the nipple, which can be difficult, and cause misfiring if not accurate.